Electronics in ICD lead- whats in it?

Hello,One idea I have had that I am interested in collaborating in is implantable Cardiac defibrillator lead mechanical design. The risk found in ICD lead extraction I have heard is due to tissue calcification, but I think there may be a clinical need for an improved design, which allows for extraction with reduced risk of emboli or tissue damage. What I don't know much about is the electronics. Does anyone know what electronics are in there?feel free to PM